Option to run a fixed number of cycles

Ad an option to allow only a specific number of cycles (or fractions of a cycle) to run before stopping automatically.
Also fixed a bug that did not allow for multiple instance to be used together.

Better servo pin management

Allow setting servo independent of attaching/detaching.

The pin connected to the servo can now be managed without having to
attach to the servo first. The pin can also be kept for the ServoOsc
instance even after detaching.
This allows users of the library to have the ServoOsc instance save and
manage the pin independently of being attached/detached to/from the
servo, instead of having to keep a separate variable to manage the pin.

Updated all documentation and examples to use the new setPin(),
attach(), detach(), getPin(), isAttached(), etc. methods.

Better documentation

v1.0.1

Add keywords.txt and bump the patch level version

First release

v1.0.0

First commit